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ZeeTso[_3_] ZeeTso[_3_] is offline
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Default horizontal tubes

hi!

i have no previous experience in building tube amps, and for my first
project i want to build small 5W guitar/bass amp head.
it will be simplified version of h&k b.a.t.t.:

http://hughesandkettnermicroamps.wee...ss-master.html

i'm a bit concerned about horizontal tube position which is necessary in
order to achieve low profile design that i'm lookin for.

is there any serious drawback with tubes if they are used like that?

tnx!


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Patrick Turner Patrick Turner is offline
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Default horizontal tubes

On Friday, 14 September 2012 23:01:03 UTC+10, ZeeTso wrote:
hi! i have no previous experience in building tube amps, and for my first project i want to build small 5W guitar/bass amp head. it will be simplified version of h&k b.a.t.t.: http://hughesandkettnermicroamps.wee...ss-master.html i'm a bit concerned about horizontal tube position which is necessary in order to achieve low profile design that i'm lookin for. is there any serious drawback with tubes if they are used like that? tnx!


The 12AX7 and EL84 are OK horizontal. But I am concerned that because the amp box is a flat shallow box like those used for 1,001 solid state amps, ppl could forget to keep the ventilation holes in the top plate un-obstructed by CDs, books, and much other junk that ppl put dowen on an available flat surface in a crowded messy evironment. Left turned on with something covering vent holes, expect temperature to rise alarmingly on warm days and hence the electrolytics may become damaged and other things may go wrong. No electronic circuits like working at say 85C or higher for long periods so make sure venitlation is OK.
If T goes high, one often sees that the plastic label wrap around electro caps can shrink and split. The caps keep working, but have a reduced life. So the wrapping shrink can indicate how hot things are getting in the box.

I'l try not to be stupid by saying the horizontal tubes sound best when playing geetah lying down, and best listened to in bed. Many guitar amps have their tubes monted vertically, but upside down so of course for those amps you must play better if you stand on your head, and listen while strung up by your feet.

Patrick Turner.
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Don Pearce[_3_] Don Pearce[_3_] is offline
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Default horizontal tubes

On Fri, 14 Sep 2012 07:50:01 -0700 (PDT), Patrick Turner
wrote:

On Friday, 14 September 2012 23:01:03 UTC+10, ZeeTso wrote:
hi! i have no previous experience in building tube amps, and for my first project i want to build small 5W guitar/bass amp head. it will be simplified version of h&k b.a.t.t.: http://hughesandkettnermicroamps.wee...ss-master.html i'm a bit concerned about horizontal tube position which is necessary in order to achieve low profile design that i'm lookin for. is there any serious drawback with tubes if they are used like that? tnx!


The 12AX7 and EL84 are OK horizontal. But I am concerned that because the amp box is a flat shallow box like those used for 1,001 solid state amps, ppl could forget to keep the ventilation holes in the top plate un-obstructed by CDs, books, and much other junk that ppl put dowen on an available flat surface in a crowded messy evironment. Left turned on with something covering vent holes, expect temperature to rise alarmingly on warm days and hence the electrolytics may become damaged and other things may go wrong. No electronic circuits like working at say 85C or higher for long periods so make sure venitlation is OK.
If T goes high, one often sees that the plastic label wrap around electro caps can shrink and split. The caps keep working, but have a reduced life. So the wrapping shrink can indicate how hot things are getting in the box.

I'l try not to be stupid by saying the horizontal tubes sound best when playing geetah lying down, and best listened to in bed. Many guitar amps have their tubes monted vertically, but upside down so of course for those amps you must play better if you stand on your head, and listen while strung up by your feet.

Patrick Turner.


Electrolytic capacitor lifetime is an important factor in equipment
that runs hot.

Look up your electrolytic to find its data sheet. You need two figures
- maximum temp, which could well be printed on the side, and lifetime
- which will be several thousand hours, probably.

That lifetime assumes the cap is running at the maximum temperature.
After several hours of running, measure the actual temperature of the
cap at its hottest point. You can now calculate an expected lifetime
simply.

hours(expected) = hours(specified) * 2 ^((Tmax-Tactual)/10)

And that's it. Hopefully your 3000 hours will become much bigger.

d
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Phil Allison[_3_] Phil Allison[_3_] is offline
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Default horizontal tubes


"ZeeTso"

i have no previous experience in building tube amps, and for my first
project i want to build small 5W guitar/bass amp head.
it will be simplified version of h&k b.a.t.t.:

http://hughesandkettnermicroamps.wee...ss-master.html

i'm a bit concerned about horizontal tube position which is necessary in
order to achieve low profile design that i'm lookin for.

is there any serious drawback with tubes if they are used like that?



** Only that the EL84 may get too hot due to lack of ventilation.

If you fit a 35mm fan, blowing directly on the EL84 - problem gone.

http://sigma.octopart.com/9362392/im...5PFV2-8.GN.jpg

Such a fan can be mounted internally and simply stirs the air inside around
your case - warming everything by a few degrees while cooling the EL84.


.... Phil


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John L Stewart John L Stewart is offline
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Quote:
Originally Posted by ZeeTso[_3_] View Post
hi!

i have no previous experience in building tube amps, and for my first
project i want to build small 5W guitar/bass amp head.
it will be simplified version of h&k b.a.t.t.:

http://hughesandkettnermicroamps.wee...ss-master.html

i'm a bit concerned about horizontal tube position which is necessary in
order to achieve low profile design that i'm lookin for.

is there any serious drawback with tubes if they are used like that?

tnx!
I built this little amplifier back in 1968. Since then it has been used in quite a wide variety of locations. For the past few years it has been in my workshop. Program sourc-es are an Eico HFT-90 FM receiver and a matching Eico HFT-94 AM receiver.

The electronics is a FB pair consisting of a 6AU6 & 6AQ5 driving into a Hammond 125D OPT. The front end is a 12AX7 connected as a Baxandall tone circuit & another 12AX7 as a preamp for a low level magnetic phono pickup up or can be switched to a mike. DC is supplied by a FW SS rectifier driven by a Hammond 270AX transformer.

I managed to build the entire amp, tone controls, and preamp into a Hammond 8 × 12 × 3 chassis. Most of the major com-ponents are on a 3 × 12 sub-chassis inside. That includes the power supply, power amp, preamp, and tone circuits. I assembled the sub-chassis on the bench. The controls, input, and output connections are mounted on the front and rear panels of the chassis. These were all wired together at the final assembly stage.

Because there is some heat to be dis-sipated, I used a set of four 1˝ diameter ventilation hole plugs mounted on the ends of the chassis. There are several ½˝ holes in the bottom plate to allow cooling air in.

Around 1960 I built two other complete amps inside the larger Hammond 8 x 16 x 3 chassis. Both were running PP 25L6’s into Hammond 125D OPT’s. Other tubes in the lineup consisted of the regular 6SL7 type preamps & drivers. They were used by friends & never came back due to failures.

All these amps ran with the tubes mounted horizontally inside the chassis without problems. So far no electrolytic failures to report but something to consider in a poorly ventilated environment. But as Patrick T has commented, don’t leave a book on top. Something not likely on a guitar amp, anyway.

Good luck with your project, John
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